I love the thick wool felt that's increasingly popular, but man. Wool felt in the 3mm to 5mm range is really expensive ($130/yard or so). The boxes, bowls, and vessels made with it are very cool, though. So when I was poking around my local craft store, I found a poor girl's substitute: Eazy Felt. You know it's cheap when "easy" is spelled with a Z instead of an S on the product label. It's regular craft felt that's been stiffened into sturdy sheets, and cost me $1.78 per 12"x18" sheet.
To make felt boxes, I cut a 9" square for the bottom piece, then added four slits and four diagonal cuts to trim away some of the excess felt on the tabs. See my template here.
I used a rotary cutter and ruler to cut out the main shape, then made the slits and diagonal cuts with an X-acto knife. The stiffened felt cuts quite eazily. I didn't trace a pattern onto the felt; just measured with a ruler, marked the points, and sliced.
The box top is similar, except the center area is larger to fit over the box bottom, and the sides are half the height. See the template here.
After the pieces are cut, crease the tabs against the edge of a ruler to make assembly easier.
Fold the triangular tabs inward and bring the sides of the box up. (To allow for the thickness of the felt, you may need to trim an eighth inch off the edge of the triangle tabs so they don't poke out past the sides of the box.) Then secure the flaps with a hot glue gun. Do the same for the box lid. All done!